This invention relates to improvements in variable speed transmission devices and more particularly, it concerns an improved transmission of the type in which torque is transmitted by rolling frictional engagement at two points of contact between a pair of first and second elements having surfaces of revolution angularly disposed on intersecting first and second axes, the first element being rotatable on the first axis whereas the second element nutates so that the second axis revolves in a bi-conical path about the first axis.
In a co-pending application for U.S. Pat. Ser. No. 706,291, filed July 19, 1976 by Yves Jean Kemper, there are disclosed several embodiments of a transmission in which a gyroscopic force couple is deployed at two points of rolling friction contact between a first element rotatable on its own axis and a second element having an axis revolvable about the first axis in a bi-conical path such that the second element undergoes nutational movement with respect to the first. In certain embodiments, the gyroscopic force couple is deployed to develop the normal force necessary to retain the rolling surfaces of the respective first and second elements in frictional engagement with each other whereas in other embodiments, the normal force required for frictional engagement is developed by mechanical means opposed by the gyroscopic force to minimize the load-supporting requirements of bearings used in the transmission. While both forms of the transmission, as thus characterized, have demonstrated great potential from the standpoint of providing an exceedingly well-balanced, variable speed torque transmission requiring a small number of easily machined components, the latter form in which the gyroscopic force couple opposes a mechanically induced normal friction force couple has shown particular promise because of the facility it provides for reducing both size and friction losses in bearings used to support the respective first and second elements.
Variation in angular velocity between an input shaft and an output shaft of such a transmission is effected by providing the rolling friction surfaces coupled to one of the shafts on a pair of generally conical members each having an apex half-angle approximately the same as the angle between the intersecting axes of the first and second elements. The conical surfaces converge from the point of first and second element axes intersection and are movable in the direction of convergence into engagement with annular rings carried by the second elements. The rings also are axially adjustable on the second element so as to engage the conical members at varying radial distances from the axis of the conical members. Inasmuch as the annular rings are of a fixed radius, the speed ratio of input and output shafts connected to the respective first and second elements will vary with the radius of the conical members at the point of rolling friction engagement.
Although various control devices are disclosed in the aforementioned co-pending application for controlling the axial positioning of the annular rings carried by one or the other of the first and second elements, the annular rings as well as the control mechanism for their axial adjustment represent an added number of components in the overall basically simple transmission. Accordingly, there is room for improvement particularly from the standpoint of reducing components necessary to the attainment of the variable transmission speed ratios.